Add support for customizing the ProtoLogDataSource name for testing

In testing environments we want to be able to test the trace without existing always on or automatically enabled tracing interfering with the test. This allows us to make sure the testing tracing happens in a unique independent datasource.

Flag: TEST_ONLY
Test: atest InternalTests:com.android.internal.protolog.PerfettoProtoLogImplTest
Change-Id: Ieb380dc9756792436beb3ff3d13ada23acf8cdd7